1. Field of the Invention
The present invention relates to the field of tone detection and, more particularly, to the detection of dual tone multi-frequency (DTMF) tones in software based telecommunications systems.
2. Description of Related Art
Modem telecommunications systems are becoming increasingly software based and typically require only a minimum of physical hardware. Much of the necessary telecommunication functionality is now provided by software functions running on powerful computer servers, such the HP OpenCall Media Platform (OCMP), running on a HP UX server. The HP OCMP, for example, is capable of handling thousands of telephone calls simultaneously and provides advanced telephony services. As the migration to software-based systems continues, it is becoming increasingly desirable, to have as much as possible of the necessary functionality provided by software, systems. This brings advantages such as the ability to upgrade and update software systems without requiring changes in the underlying hardware.
However, many functions, which are efficiently handled by dedicated hardware solutions require extensive computation and processing power when performed in software systems.
In software systems, many software functions and tasks share resources provided by a single processing platform. Consequently, processing functions which require extensive computation and processor power can cause a reduction in performance of other functions and tasks running on the same platform. Accordingly, even small differences in overall processing efficiency can make a substantial difference, for example, to the number of telephone calls, which can be handled simultaneously by a telecommunications system.
Dual tone multi-frequency (DTMF) detection is a common function that is required by telecommunications systems and is one such function that requires extensive processing resources.
The use of DTMF tones has revolutionised call placing, interactive telecommunications applications and has enabled advanced services such as telephone banking, telephone ordering services, call waiting facilities, to name but a few.
DTMF tones are transmitted over the voice circuit of a telephone network and must be accurately detected and decoded by DTMF decoding equipment. Since there is no way of knowing in advance when a DTMF tone may be present in a voice signal, the voice signal must be constantly processed to detect the presence of any DTMF tones. Numerous dedicated hardware solutions exist for performing DTMF detection, such as the Holtek HT9170 tone receiver integrated circuit, and such solutions have been used for many years in conjunction with existing hardware-based telecommunication platforms.
Although the amount of processing resources required for detecting DTMF tones does not necessarily pose a problem when processing a single off-line signal, processing efficiency becomes critical in real-time telecommunications systems handling thousands of telephone calls simultaneously.
Software DTMF detection techniques are known as such, for example as disclosed in U.S. Pat. No. 5,694,466 to Xie et al. In U.S. Pat. No. 5,809,133 to Bartkowiak et al. a DTMF tone detector is disclosed which uses the Goertzel algorithm for detecting DTMF tones. Only a portion of the Goertzel algorithm is performed for each of the possible tone frequencies, and the algorithm is then continued only on a number of selected frequencies.
The present invention is directed to improving the processing efficiency required for the software detection of DTMF tones.